Multi-mode hydrostatic transmission

ABSTRACT

A gearless split torque (mechanical/hydrostatic), twin range (reduction/overdrive) with a direct mechanical drive in-between, hydrostatic transmission with regenerative braking and engine starting capabilities comprising two hydraulic pumps tied together by a clutch.

BACKGROUND OF THE INVENTION

This application is a continuation in part of my copending applicationSer. No. 875,731 filed on Feb. 6, 1978.

Due to the limited supply of gasoline and its corresponding high cost,the importance of minimizing fuel waste in vehicles has taken newdimensions in recent years.

Presently automobiles waste fuel in several ways, some of which are:

1. During braking the vehicle's kinetic energy is transformed to heatwhich is dissipated to the surroundings.

2. When moving in congested traffic, the engine operates veryinefficiently and is running continuously even when the vehicle isstanding.

3. Present transmissions usually have a few fixed ratios vs. aninfinitely variable transmission which can continuously provide anoptimal ratio. Further, present day automatic transmissions introduceadditional power losses in the torque converter and hydraulic pumpareas.

An object of the present invention is to provide a transmission whichwill eliminate the above and other inefficiencies.

The advantages of regenerative braking, intermittent engine operation atan optimal speed and an infinitely variable transmission, as well as thevalue of these features to the fuel economy of a vehicle, are all know.However, to date, no system could be built that will provide thesefeatures without introducing undesirable and intolerable side effects ofcost, complexity and bulk.

SUMMARY OF THE INVENTION

The present invention relates to a gearless hydrostatic split torque,(mechanical/hydrostatic), twin range (reduction mode/overdrive mode)with a direct mechanical mode in-between, automotive power transmissionwhich is adapted to incorporate regenerate braking and engine startingability in one simple, compact, light and inexpensive hardware package.

The transmission is adapted to operate in several modes in order tomaximize fuel economy in various driving conditions: over the highwaythe transmission provides a direct mechanical drive (lock-up); whendescending a long incline it operates in over-drive; in the city thetransmission provides added hydrostatic torque; and in stop-and-gotraffic the transmission is fully hydrostatic, enabling the engine tooperate intermittently, charging an accumulator at an optimal rate andshutting itself off until the accumulator is almost depleted, at whichpoint the transmission restarts the engine which recharges theaccumulator.

During braking the transmission efficiently converts the vehicle'skinetic energy to pressurized fluid stored in the accumulator, to bereused for accelerating the vehicle later on or for some other neededfunction.

While all the above features and their economical value is wellestablished in the art, as mentioned previously, the unique aspect ofthe combination of the present invention is that it achieves all thesegoals without introducing unacceptable side effects of complexity, costor bulk. On the contrary, it provides all these features with a systemwhose hardware is substantially simpler than present day automatictransmissions. Further, the present system eliminates the conventionalstarting system, part of the braking system and it does the majority ofactual braking.

It can also be appreciated from the foregoing specification that the twopumps, which are combined in a unique way to form the transmission, aresimilar to conventional piston pumps. Thus, the present invention doesnot require any unproven or non-existing technology or manufacturingprocesses.

The control,specific construction whereof is not within the scope of thepresent invention, can incorporate an electronic micro-processor totranslate driver's inputs through the brake accelerator and gear shiftlevers to optimal setting of the transmission and engine elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of a transmission according to thepresent invention, and

FIG. 2 is a cross-sectional view along line 2--2 marked on FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show a hydrostatic transmission 10 adapted for a pluralityof operational modes, comprising:

A first variable displacement pump 11 having a first section serving asa mechanical input member 9 of the transmission, a second section 13, aninlet port 14 and an outlet port 15.

The first section of the first pump comprises a shaft 16 rotatablysupported by a housing 17 through a ball bearing 18. The shaft carriesand rotates with a swash plate 19 which is pivotally inclined about anaxis 20 (carried by the shaft) by a servo-actuator 21 (which alsorotates with the shaft). The actuator is operated by pressurized fluiddirected to its cavity 22 through a passage 23 and a slip ring 24. Theshaft defines inlet and outlet passages 25 and 26, respectively, whichcommunicate with the ports 14 and 15 via the slip ring.

The second section of the first pump comprises a drum 27 defining sixcylinders 28 in which pistons 29 are slidably disposed. Each piston hasa shoe 30 which slides against the swash plate 19.

A band brake 31 is actuated by a cylinder assembly 32 in response topressurized fluid communicated to it by a conduit 33 from a control 47.

A second variable displacement pump 40, having a first portion 41serving as a mechanical output member of the transmission, is coupled tothe second section 13 by a one-way clutch 42 and a flange bearing 74. Asecond portion 43 of the second pump is anchored to the housing.Numerals 44 and 45 indicate suction and discharge ports, respectively.(As will be discussed later either pump serves as a motor in some of theoperational modes, and commonly pumps can reverse their role in thismanner. However, to avoid confusion, assemblies 11 and 40 will bereferred to as "pumps" throughout the text of this applicationregardless of whether they convert mechanical energy to pressurizedfluid flow or vice versa).

An accumulator 46 is adapted for storing fluid under pressure.

The control 47 is connected to ports 14, 15, 44, 45 and to theaccumulator through conduits 48, 49, 50, 51 and 52, respectively. Thecontrol is also connected to a brake pedal 70, an accelerator pedal 71and a shift lever 72 and to an engine (not shown).

The first portion of the second pump is similar to the second of thefirst pump, and comprises a drum 53 and pistons 54 (each piston is urgedoutwardly by a spring 55, one shown). The drum 53 has a gear 56 affixedto it by a weldment 75 and serves as an output member of thetransmission. The drum 53 is rotatably supported by a ball bearing 57.

The second portion of the second pump comprises a center post 58defining suction and discharge passages 59 and 60 respectively (similarto the inlet and outlet passages of the first pump) which communicatewith the ports 44 and 45 respectively. A swash plate 61 is pivotallyinclinable about an axis 62 by a cylinder assembly 63 which iscontrolled by pressurized fluid communicated to it by a conduit 64 fromthe control 47. The gear meshes with a ring gear 65 of a differential 66which in turn drives right and left wheels (not shown) through axles 67and 68 respectively.

The engine (not shown) drives the transmission mechanical input member16.

OPERATION

The present transmission is adapted to operate in a plurality of modesas a transmission, and in addition as a regenerative brake and as anengine starter. These various operational modes will be reviewed herein:

Direct lock-up mode is achieved by inclining the swash plate 19 and bythe control 47 blocking the outlet port 15 in the control 47 or byconnecting it to one of the second pump ports 44 or 45, and cancellingthe inclination of the swash plate 61. This locks the two sections ofthe first pump one to the other, and in this mode the power istransmitted directly from the mechanical input member 16 through thefirst pump 11, through the one-way clutch 42 to the mechanical outputmember. This mode of operation is well suited for highway travel, etc.In the direct mode, 100% of the power is conveyed mechanically and thetransmission's efficiency is closed to 100%. The speed ratio and torqueratio are practically both 1 to 1.

Reduction mode is achieved by inclining both swash plates and connectingthe outlet port 15 to the suction port 44. To illustrate this mode, itwill be assumed that the engine and the mechanical input member rotateat 2000 RPM and the mechanical output member rotates at 1000 RPM. Thatis a 2:1 speed reduction and close to a 2:1 torque multiplication. Itcan be observed that the relative speed between the swash plate and thedrum in both pumps is 1000 RPM and since the pumps are in a seriesconnection, this means that they are set in this speed ratio at equaldisplacements per revolution (ignoring volumetric inefficiencies, etc).

In this mode the power is split. The engine's full torque is conveyedmechanically from the mechanical input to the output member, exactly asin the direct mode. The relative rotation occuring in the first pump 11is translated to pressurized fluid flow which is translated to anadditinal torque of the mechanical output member by the second pump 40.

With an increase of the volume per revolution of the second pump 40 vs.the first pump 11, the transmission's speed ratio decreases andvice-versa. In all these ratios, the torque at the mechanical outputmember is the sum of the engine's torque, which is passed mechanicallythrough the transmission exactly as in the direct mode, plus theadditional torque generated by the second pump 40. The inefficiency thattypifies hydrostatic transmissions applies only to the part of the powerwhich is conveyed hydrostatically to generate this additional torque.

Thus, the overall efficiency of the transmission, especially when usedin a direct mode, or a ratio close to direct mode, a substantial part ofthe time, can be very high.

Overdrive mode is achieved by inclining both swash plates and connectingthe discharge port 45 to the outlet port 15. In this mode, part of theengine torque is passed mechanically through the first pump to thesecond pump to generate pressurized fluid which is used by the firstpump to rotate both drums (which are coupled by the one-way clutch 42)at a speed over engine speed. Thus the torque is reduced and the speedis increased between the mechanical input and output members. In thismode, as in the reduction mode, the power is split with the hydrostaticinefficiency applicable only to the part carried hydrostatically. Theimportance of the over-drive mode is that it permits one to design thedirect ratio to be in the middle of the ratio range which is in heavystatistical usage, thereby improving the overall efficiency of thetransmission.

As can be seen in this mode the outlet port 15 receives pressurizedfluid, however, for consistency of description the names of the portswhich were coined in relation to their function in the reduction modeare used throughout the text to avoid confusion. It can also be notedthat instead of physically switching and/or blocking ports one can shiftthe transmission continuously from the reduction mode through the directmode to the overdrive mode by cancelling the inclination and byreversing the inclination, respectively, of the swash plate 61 sincecancelling the inclination makes the second pump 40 act as a blockage tofluid flow between its ports 44 and 45, and since reversing theinclination reverses the ports' function. It can be further noted thatwhile either of these methods would work there are structural andefficiency considerations which may cause a designer to prefer onemethod over the other.

Regenerative braking mode is accomplished by connecting the dischargeport 45 of the second pump 40 to the accumulator. The braking torque isincreased or decreased by increasing or decreasing, respectively, theinclination of the swash plate 61. Thus, the kinetic energy of thevehicle is efficiently transformed to fluid under pressure in theaccumulator, which can be reused to reaccelerate the vehicle.

Engine starting mode is accomplished by actuating the band brake 31 toanchor the drum 27, and by connecting the charged accumulator to theinlet port 14 of the first pump 11 which rotates the mechanical inputmember and the engine which is coupled to it.

Hydrostatic mode is accomplished by anchoring the drum of the first pumpwith the band brake 31 and by connecting the output port 15, the suctionport 44 and the accumulator to one another. In this mode, the controlcauses the engine to work intermittently at a certain optimal speed,charging the accumulator. When the accumulator is charged, the controlshuts off the engine and the car continues to move, accelerate, stop,etc. on power supplied from the accumulator.

When the accumulator is depleted to a certain level of its energystoring capacity, the control connects the input port 14 to it, causingthe first pump to restart the engine (as previously explained) andrecharge the accumulator.

This mode of operation is most suitable for moving in stop-and-go orvery slow traffic.

Reverse mode is achieved by inclining both swash plates and connectingthe discharge port 45 to the outlet port 15, as in the overdrive mode.However, in the reverse mode the relative inclination of the swashplates 19 and 61 is such that the displacement per revolution of thesecond pump 40 is greater than that of the first pump 11, whereas in theoverdrive mode the opposite is true.

The one-way clutch 42 can be substituted or tied in series to aselectively actuatable clutch, which, in the reverse mode, wouldcircumvent the coupling of the one-way clutch 42. This would allow thereverse mode to be carried out as a part of the hydrostatic mode, at animproved efficiency. However, in most road vehicles the reverse mode israrely used, and therefore compromising its efficiency may beacceptable. An advantage of the one-way clutch is that it isautomatically self-energized.

Hybrid-mode is one of the previously discussed modes (other than thehydrostatic mode), which like the hydrostatic mode, is modified tomaintain the accumulator charged by metering into it pressurized fluidfrom the transmission. The continuous availability of hydraulic powerallows the design of the vehicle's auxilliary power driven units such asalternator, fan, air-conditioning compressor, etc, to be hydraulicallyand selectively driven, rather than mechanically driven by the engine.This arrangement has some advantages in allowing the location andregulation of the speed of these auxilliary units independent ofengine's location and speed.

While the present invention has been illustrated with a singleembodiment, it will be appreciated that modifications and substitutionscan be made without departing from the spirit of the invention and thescope of the claims.

I claim:
 1. A hydrostatic transmission adapted for a plurality ofoperational modes, comprising in combinations:a. a first pump having afirst section serving as a mechanical input member of said transmission,a second section, an inlet port and an outlet port, b. a second pumphaving a first portion serving as a mechanical output member of saidtransmission and coupled to said second section by clutch means, asecond anchored portion, a suction port and a discharge port.
 2. Atransmission as in claim 1 having control means connected to said portsvia conduits.
 3. A transmission as in claim 2 having an accumulator forstoring fluid under pressure connected via conduits to said controlmeans.
 4. A transmission as in claim 1 wherein said clutch meanscomprise a one-way clutch.
 5. A transmission as in claim 1 wherein atleast one of said pumps is a variable displacement pump.
 6. Atransmission as in claim 2 wherein said control means blocks said outletport to effect a direct coupling of said mechanical input member to saidmechanical output member.
 7. A transmission as in claim 1 wherein saidcontrol means connects said outlet port to said suction port to effect areduction ratio.
 8. A transmission as in claim 1 wherein said controlmeans connects said discharge port to said outlet port to effect anoverdrive ratio.
 9. A transmission as in claim 3 wherein said controlmeans connects said discharge port to said accumulator to effectregenerative braking of said mechanical output member.
 10. Atransmission as in claim 3 with brake means for selectively anchoringsaid second section while said control means connects said inlet port tosaid accumulator for rotating said mechanical input member.
 11. Atransmission as in claim 3 with brake means for selectively anchoringsaid second section while said control means connects said outlet port,said suction port and said accumulator together to effect a hydrostaticmode.